Research on Gas Extraction and Cut Flow Technology for Lower Slice Pressure Relief Gas under Slice Mining of Extra-thick Coal Seam

Abstract

For extra-thick coal seams, slice mining is a safer mining method than top coal mining, which can effectively reduce the strong mine pressure behavior caused by mining. However, in the slice mining of high-gas and extra-thick coal seams, the gas in the lower slice flows into the goaf, which increases the gas control difficulty on the upper slice working face. It is easy to cause the gas transfinite at the upper corner in the upper slice and reduce the mining efficiency. Therefore, it is of a great significance to carry out the research on gas control technology in slice mining of the extra-thick coal seam. There are some problems in the gas control of slice mining, such as a single gas control method, low control efficiency, and unclear gas migration law. Therefore, it is necessary to study the gas migration law and propose a targeted prevention and control the technical scheme. In order to improve the gas control efficiency of the extra-thick coal seam, the evolution law of permeability of the lower slice is obtained under mining through experimental research. The liquid–solid coupling seepage-flow model for gas migration is established in the lower slice. Comsol Multiphysics software is used to study the migration law of pressure relief gas in the lower slice. Based on the gas migration law, the gas extraction and cut flow technology for the lower slice long borehole is proposed. Through this technology, the amount of gas flowing into the upper slice goaf and the gas content of the lower slice are reduced, and the drilling horizon is optimized. The research results show that the determination of the optimal drilling horizon of the lower slice needs to balance the amount of gas flowing into the goaf and the total amount of gas extraction. The range of 3–7 m horizon in the lower slice is appropriate to the boreholes arranged. When the borehole is located in the lower slice −3 m horizon, the 360 day gas emission quantity of goaf can be reduced to 51.2% of the nondrilled emission quantity, and the total extraction amount is 1143 m 3 . When the borehole is located in the lower slice −7 m horizon, the 360 day gas emission quantity of goaf can be reduced to 95.31% of the nondrilled emission quantity, and the total extraction amount is 1461 m 3 . Considering the gas emission capacity of the upper slice and ensuring that the total extraction volume of the lower slice is maximized and the boreholes in the lower slice are not damaged, the boreholes are located in the −6 m horizon of the lower slice.

Substantiation of Drilling Parameters for Undermined Drainage Boreholes for Increasing Methane Production from Unconventional Coal-Gas Collectors

“…Moreover, one of the recent studies [105] convincingly proved the relationship between pressure release and the growth of methane concentration from 4 m after the longwall passage in the Tingnan Coal Mine (China). At the same time, the fact [106,107] that the dynamics of methane emission directly depends on changes in the concentration of gas in the extracted mixture indicates an obvious opportunity to use the latter as a "connecting link".…”

Study on the Application of Comprehensive Gas Control Technology for Source-Separated Three-Dimensional Gas Extraction in Large Mining Faces

“…In recent years, with the advancement of gas extraction technology, there has been an increasing diversification of gas management methods. Shi 6 researched the gas management technology for the slice mining of extra-thick coal seams. Li 7 investigated the application effectiveness of directional hydraulic fracturing technology in low-permeability coal seams; Yang 8 proposed the use of water–gas combined methane control technology to improve the permeability of low-permeability coal seams near faults.…”